I have just finished reading and absorbing (twice) Ken
Dial's long-awaited paper, and have a
query/observation for you.
Ken Dial proposes that wing-assisted incline running
(WAIR) was a pivotal stage for theropod flight.
However: is it not logical to assume that
wing-assisted incline locomotion arose AFTER theropods
had developed nascent flight rather than precipitating
flight?
As you pointed out in your DML letter of 16 January,
"WAIR behavior is asociated with predator escape" in
living dinosaurs, and I would assume this held, as
well, for pre-K/T basal Eumaniraptora.
However: if these small taxa (with lateral oriented
glenoids + elongate arm feathers + wide sterna, as you
illustrate) needed to rush up inclines (be it cliffs
or trees) faster than predators chasing them, then
would not these taxa have (re)evolved elongate arms
for running and climbing to escape the predators?
Moreover: once theropod flight began, then WAIR
behaviour makes perfect sense, i.e., when being
chased, they would use their wings to "climb" to
escape predators (the wings providing an added "boost"
to already powerful running legs). Over time, this
ability (as documented by Ken Dial) would be
ontogenetic physiological homeostasis for these
dinosaurs, reinforced by genetic drift to preserve the
mechanisms (setting aside the probability theropod
parents taught their chicks by example).
In other words: AFTER flight had begun in theropods,
WAIR behaviour would be self-reinforcing processes
(Stephen Gould calls these processes "differential
speciation...Frequent correlation of directional
speciation with differential proliferation"),
accelerating the evolution of flight itself. Flight,
thus, enabled these small dinosaurs to reach higher
places not accessible by predators (assuming they were
not flying after them). Thus, in dinosaur evolution,
WAIR behaviour would be a need/utility amplification
of wings/flight in Theropoda.
WAIR and flight seem intertwined after the appearance
of the evolutionary novelty of feathers. Evolution
transpires when variant offspring, perhaps due mostly
to environmental stresses, can survive (i.e., have
heightened acuity of immune systems), breed, pass
character traits of the genome on to offspring
(Stephen Gould's "agency, efficacy, and scope" are
what I have in mind, or the Gould/Vrba idea of
"sorting"/selection-and-drift). "Selection", thus,
would be causalities of interrelationships of genomes
(traits, etc.) and environments, as well as drift
(Vrba's 1980 "the effect hypothesis", e.g.).
Dinosaurs, then and now, are biomolecular structures
of organic compounds...and, without WAIR behaviour, I
do not think flying (or secondarily flightless)
dinosaurs would have survived beyond the
end-Cretaceous. Why? Because, by using WAIR behaviour,
these dinosaurs could construct nests up in trees, or
in burrows on the sides of cliffs, beyond the reach of
tyrannosaurs, compsognathuses, and ornithomimids (like
you, I am most curious if WAIR behaviour was present
among baby troodonts and velociraptors (including
Deinonychus), etc.).
What do you think?
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